The present invention relates generally to a method and apparatus for treating the surface of a substrate and more particularly to a method and apparatus for electroplating a layer on a semiconductor wafer.
The manufacture of semiconductor devices requires the formation of electrical conductors on semiconductor wafers. For example, electrically conductive leads on the wafer are often formed by electroplating (depositing) an electrically conductive material such as copper on the wafer and into patterned trenches.
Electroplating involves making electrical contact with the wafer surface upon which the electrically conductive material is to be deposited (hereinafter the xe2x80x9cwafer plating surfacexe2x80x9d). To insure a uniform deposition, it is important that the electrical contact with the wafer plating surface be uniform and reliable.
Brogden et al., U.S. Pat. No. 5,227,041 (hereinafter Brogden), teaches a dry contact electroplating apparatus wherein a number of electrical contacts are provided adjacent to a central aperture of a base of the apparatus. Brogden further teaches that the contacts preferably include relatively-sharp tips for piercing any insulating substance which may be present on the wafer plating surface. However, even with relatively sharp tips, one or more of the contacts may form a poor electrical connection with the wafer plating surface. This results in nonuniformity of the deposited electrically conductive layer. To determine if one or more poor electrical connections were made with the wafer plating surface, the wafer can be-tested to measure the uniformity of the deposited electrically conductive layer. However, wafers exhibiting nonuniformity of the deposited electrically conductive layer must be discarded reducing the yield of the electroplated wafers. Further, it is not practical or cost effective to test every wafer. Thus, it is desirable to have an apparatus for electroplating a wafer which provides uniform electrical contact with the wafer plating surface while at the same time providing a means of readily testing the integrity of the electrical contact with the wafer plating surface before the wafer is electroplated.
Electroplating also requires immersion of the wafer in a plating solution (i.e. a solution containing ions of the element being deposited, for example a solution containing Cu++). It is important to prevent contamination of the wafer backside (i.e. the surface of the wafer opposite the wafer plating surface) and the wafer edge from the electrolyte (the ions of the element being deposited).
One conventional method of preventing contamination is to use a corrosive solvent immediately following the electroplating to remove contaminants from the wafer backside and the wafer edge. While this method is satisfactory, it requires an extra processing step and the use of hazardous chemicals. A more effective method is to prevent contamination of the wafer backside and the wafer edge in the first place. Accordingly, it is desirable to have an apparatus for electroplating a wafer which avoids contamination of the wafer backside and the wafer edge at any time during the process.
Brogden (cited above) teaches an electroplating apparatus which reduces contamination of the wafer backside and wafer edge during the electroplating process. Referring to FIG. 2 of Brogden, a sealing ring 40 positioned inside electrical contacts 36 forms a sealing connection with the wafer so that contacts 36 and the wafer backside and edge are not exposed to the plating solution. However, particulates and nonuniformities may result in a poor sealing connection with the wafer allowing plating solution to leak past sealing ring 40 to contaminate contacts 36 and the wafer backside and edge. In the event of leakage, the electroplating apparatus must be serviced and the wafer may have to be discarded. Accordingly, the art needs a dry contact electroplating apparatus which eliminates possible leakage of the plating solution and avoids the associated contamination of the contacts and wafer backside and edge.
Another difficulty with immersing the wafer in a plating solution is entrapment of air bubbles on the wafer plating surface. Air bubbles disrupt the flow of electrolytes and electrical current to the wafer plating surface creating nonuniformity in the deposited layer. One conventional method of reducing air bubble entrapment is to immerse the wafer vertically into the plating solution. However, mounting the wafer vertically for immersion into the plating solution adds complexity and hinders automation of the electroplating process. Accordingly, it is desirable to have an apparatus for electroplating a wafer which avoids air bubble entrapment and which is automated.
In accordance with the present invention, an apparatus for treating a plating surface of a substrate, typically a wafer, includes a cup having a central aperture defined by an inner perimeter, a compliant seal adjacent the inner perimeter, a plurality of contacts adjacent the compliant seal and a cone attached to a rotatable spindle.
When the cup is clamped to the cone, an O-ring in the pressing surface of the cone presses against the backside of the wafer. This forms a seal between the O-ring and the backside of the wafer and also between the compliant seal and a perimeter region of the plating surface of the wafer while simultaneously forming the electrical connection between the plurality of contacts and the plating surface. The seal with the plating surface prevents the plating solution from contacting the wafer edge, the wafer backside and the plurality of contacts and thus prevents the associated electrolyte contamination. As a secondary measure to prevent electrolyte contamination, the region behind the compliant seal is pressurized thus preventing the plating solution from leaking past the compliant seal. Further, any leak in the seal with the plating surface can be readily detected by monitoring for any escape of the pressurized gas in the region behind the compliant seal.
Mounting the cone on a rotatable spindle advantageously allows the assembly of the cone, cup and wafer to be rotated after the assembly is immersed in the plating solution. This prevents bubble entrapment on the wafer and improves electrolyte transport to the wafer which, in turn, improves the uniformity of the electroplated layer. Further, the thickness profile of the electroplated layer can readily be adjusted by changing the rotational speed of the assembly.
The plurality of contacts can be grouped into banks of contacts electrically isolated from one another. In this manner, after the electrical connection between the plurality of contacts and the plating surface is established, continuity in resistances between the banks of contacts can be checked to readily detect if any poor electrical connections were made.
In accordance with the present invention, a method of depositing an electrically conductive layer on the wafer includes providing the wafer having an electrically conductive seed layer on a first surface of the wafer. The wafer is then placed first surface down into the cup and the cup is then clamped to the cone thus establishing the electrical connection between the plurality of contacts and the seed layer. The cup is then placed into the plating solution thus exposing a portion of the seed layer to the plating solution. The cup and wafer are then rotated and voltage is applied to the plurality of contacts thus depositing the electrically conductive layer on the seed layer.
In accordance with the present invention, a rotary union for use with an electroplating apparatus includes a shaft having a first surface area and an extended surface area, the first surface area having a first aperture therein, the extended surface area having a second aperture therein. The rotary union further includes an outer face seal and an inner face seal. The outer face seal is pressed against, and forms a seal with, the first surface area. The inner face seal is pressed against, and forms a seal with, the extended surface area. A pressure passage coupled to the first aperture passes through the outer face seal and around the outside of the inner face seal. A pressure/vacuum passage coupled to the second aperture passes through the inner face seal.
The rotary union has a lower connector or a lower connector in combination with a tube connector which allows the pressure/vacuum passage to be coupled to an inner coaxial tube and the pressure passage to be coupled to an outer coaxial tube. Of importance, this allows both vacuum and pressure to be provided through the inner and outer coaxial tubes, respectively, to a rotating clamshell of the electroplating apparatus. Since the inner and outer coaxial tubes share a common axis (the inner tube being inside of the outer tube), the space required for the tubing is reduced to that of the outer coaxial tube compared to having both the inner and outer tubes in a side by side arrangement. This is particularly advantageous for use in an electroplating apparatus in accordance with the present invention wherein size constraints of the pressure and vacuum lines, as well as concentric geometry, require coaxial tubing of the pressure and vacuum lines.
These and other objects, features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below taken in conjunction with the accompanying drawings.